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No effect Hopes that a Mediterranean diet would be as good for the head as it is for the heart may have been dampened by a French study that found little benefit for aging brains from the diet rich in fruit, vegetables, whole grains, nuts, wine and olive oil.

The study, published in the American Journal of Clinical Nutrition, looked at the participants' dietary patterns in middle age and measured their cognitive performance at around age 65, but found no connection between Mediterranean eating and mental performance.

"Our study does not support the hypothesis of a significant neuroprotective effect of a (Mediterranean diet) on cognitive function," writes study leader Emmanuelle Kesse-Guyot at the nutritional epidemiology research centre of the French national health research agency INSERM.

It's been suggested that the "good" fats in the Mediterranean diet might benefit the brain directly, or that low saturated fats and high fiber in the diet could help stave off cognitive decline indirectly by keeping blood vessels healthy.

Previous research has seemed to uphold that premise.

One large study in the US Midwest, for example, found that people in their 60s and older who ate a mostly Mediterranean diet were less prone to mental decline as they aged. Another study of residents of Manhattan linked a Mediterranean-style diet to a 40 per cent lower risk of Alzheimer's disease.

No significant difference

Researchers in the French study used data on 3083 people who were followed from the mid-1990s, when they were at least 45 years old.

At the beginning of the study, participants recorded what they ate over one 24-hour period every two months, for a total of six dietary record samples per year. Then, between 2007 and 2009 when the participants were about 65 years old, their memory and other mental abilities were measured.

Researchers then separated participants into three categories depending on how closely they adhered to a Mediterranean-style diet, and compared their mental ability test scores.

Overall, they found that people who ate a diet closest to the Mediterranean ideal performed about the same as those who ate a non-restricted diet.

Associate Professor Nikos Scarmeas, of New York's Columbia University Medical Center, was not involved with the study but has researched the effects of food on brain health. He says it's important to note that the new study had some limitations.

For instance, researchers only tested the participants' mental abilities once, making it impossible to track whether they got better or worse over time, adds Scarmeas.

"We don't have the strong evidence to go and tell people, 'Listen, if you follow this diet, it will improve cognition'," he says.